Polypropylene has excellent mechanical properties, chemical resistance, and other properties, and is very useful in view of balance against economy. Therefore, polypropylene is widely applied to a variety of molding techniques. However, moldability of polypropylene with respect to techniques such as blow molding, expansion molding, and extrusion molding is insufficient due to low melt tension and low crystallization temperature. In addition, high-speed production of a molded object through other molding techniques is limited.
Although a crystalline propylene homopolymer has high rigidity, its impact resistance has a problem remained, particularly at low temperature. In order to mitigate this drawback, there has been proposed a composition produced by forming a crystalline propylene homopolymer and subsequently forming an ethylene-propylene copolymer (a so-called block copolymer). Although the composition has improved impact resistance as compared to the case of a crystalline propylene homopolymer, the block polymer still has drawbacks such as being highly prone to whitening by impact or bending; low transparency; and large molding shrinkage.
In view of the foregoing, an object of the present invention is to provide a polypropylene composition having high melt tension, a high crystallization temperature, and excellent thermal stability and providing a molded article having excellent transparency, reduced molding shrinkage, and excellent resistance to whitening by impact or bending to mitigate the above drawbacks. Another object of the present invention is to provide a process for producing the composition.